The primary objective of the studies in this ADRN application is to improve our understanding of mechanisms underlying cutaneous host defense, by determining the cause of different phenotypes of atopic dermatitis (AD) including Staphylococcus aureus (S. aureus) colonization, eczema herpeticum (EH) and severe AD. These studies will include assessment of skin barrier, and adaptive/innate immune system responses to viral and bacterial infections, as well as genetic and epigenetic studies. Three Interventional Clinical Trials Projects with accompanying mechanistic studies are proposed. The first intervention will be aimed at modulating bacterial colonization of the skin and improving the skin host defense by microbiome transplant. The other 2 interventions will assess the effects of Th2/TSLP cytokine blockade in human AD on S. aureus colonization and vaccination responses in different skin compartments (intradermal and transcutaneous). Three Clinical Mechanistic Studies will be aimed at delineating cellular and molecular mechanisms of severe AD phenotypes, and AD subsets prone to recurrent EH, and S. aureus colonization and/or infection. Two animal protocols are also proposed to directly support clinical studies by providing a mechanistic understanding of skin host defense to alterations in microbiome, and comparing cutaneous versus non-cutaneous vaccination immune responses. The proposed protocols are as follows: 1) Targeted Microbiome Transplant in AD; 2) Effect of Dupilumab(r) (anti-IL4Ra) on the Host-Microbe Interface in AD; 3) Randomized Study of Fluzone(r) Immunogenicity after Transcutaneous Vaccination in AD; 4) A Systems Biology Approach to Identify Determinants of S. aureus Colonization in AD; 5) Integrated Extreme Trait Analysis to Understand the Etiology of Eczema Herpeticum; 6) Defining the Determinants of Disease Severity in AD of Different Races and Ethnic Groups; 7) Modulation of the Immune Response to Cutaneous Immunization in a Mouse Model of AD by S. aureus; 8) Control of Microbiome Function by the Barrier in a Mouse Model of AD. Successful completion of these 6 interrelated clinical projects, and 2 animal protocols which directly support the human research, will create a paradigm shift in our understanding of genetics, skin barrier function, microbiome, innate and adaptive immune response underlying host defense mechanisms in the skin of distinct but associated AD phenotypes. At the end of this funding period, these cutting edge mechanistic studies will be translated into new treatment approaches in AD, a disease that remains difficult to treat and that has eluded molecular characterization.